Dual thermostats having common adjusting means for establishing and maintaining preselected and variable temperature ranges



June 6, 1967 R. E. MAYO 3,323,723

DUAL THERMOSTATS HAVING COMMON ADJUSTING MEANS FOR ESTABLISHING AND MAINTAINING PRESELECTED AND VARIABLE TEMPERATURE RANGES 4 Sheets-Sheet 1 Filed Feb. 23, 1965 Reub I n E. Maya,

INVENTOR,

ATTORN E Y8 June 6, 1967 R. E. MAYO 3,323,723

DUAL THERMOSTATS HAVING COMMON ADJUSTING MEANS FOR ESTABLISHING AND MAINTAINING PRESELECTED AND VARIABLE TEMPERATURE RANGES Filed Feb. 25, 1965 I 4 sheets-skew 2 'I I hil I J "P98 I v 1 I mi -"u-- lfqulllm llQ- ,96 "W m r: A. I ll Reubi n E. Mayo,

INVENTOR,

ATTOR N EYS June 6, 1967 R MAYO DUAL THERMOSTATS HAVING COMMON ADJUSTING MEANS F ESTABLISHING AND MAINTAINING PRESELECTEI) AND VARIABLE TEMPERATURE RANGES 4 Sheets-Sheet Filed Feb. 23, 1965 ATTORNEYS R. E. MAYO VIN June 6, 1 967 3,323,723 FOR DUAL THERMOSTATS HA G COMMON ADJUSTING MEANS ESTABLISHING AND MAINTAINING PRESELECTED AND VARIABLE TEMPERATURE RANGES 4 Sheets-Sheet 4 Filed Feb. 23, 1965 FIG ll Reubi n E. Mayq INVENTOR,

ATTORNEY United States Patent G DUAL THERMUSTATS HAVING COMMON AD- .IUSTING MEANS FGR ESTABLISHING AND MAINTAINKNG PRESELECTED AND VARIA- BLE TEMPERATURE RANGES Reubin E. Mayo, R0. Box 23, Farmville, N.C. 27828 Filed Feb. 23, 1965, Ser. No. 434,474 18 Claims. (Cl. 23646) This invention relates to a thermostatic control device including dual thermostats having common adjusting means for establishing and maintaining preselected and variable temperature ranges, and which is particularly adapted for use for controlling oil burners used in the curing of tobacco.

In the curing of tobacco, and particularly bright leaf tobacco, it is important that the tobacco be maintained at a preselected temperature for a preselected period of time. When the tobacco is being cured, it is hung in a curing barn, and in such a barn, oil burners are provided to maintain the ambient atmosphere at a desired temperature. The temperature range from 80 F. to 110 F. is the range in which the color of the tobacco is changed from green to yellow, and it is crucial that this temperature range be maintained for a preselected interval of time in order to allow this color change to take place. If this time period is not maintained, and the curing temperature raises too rapidly, the tobacco Will still remain partially green, and in such a condition, it is bitter and unsatisfactory for use in cigarettes. Additionally, when the curing temperature finally reaches its upper limit of 160 F. to 170 F., it is important that a control be provided to assure that the temperature cannot go any higher, since further elevation of temperature causes the tobacco to turn red and also presents a fire hazard.

In the past, individual thermostatic units have been used in curing barns, and such individual units had to be controlled. Not only did this require a great amount of constant attention, but furthermore, there was always the chance that an operator would erroneously set the thermostat, thereby ruining the entire batch of tobacco being cured. Moreover, utilizing individual thermostats, if one such thermostat broke or became otherwise inoperative. the temperature within the curing barn could quickly rise above its preselected range, thus ruining the batch of tobacco and even presenting the possibility of a fire hazard. 1

With the foregoing matter in mind, it is, therefore, a primary object of the present invention to provide an improved thermostatic control device which is particularly adaptable for controlling oil burners used in curing tobacco.

Another primary object of the present invention is to provide a thermostatic control device wherein a single manual setting of the device controls a range of temperatures rather than merely a single temperature.

Another object of the present invention is to provide a thermostatic control device having a pair of thermostatic units therein and wherein one unit acts as a high temperature limit safety device in case the other unit should fail during operation.

Another object of the present invention includes the provision of a thermostat device wherein a single control member can be used to conjointly control two thermostatic units.

Further objects of the present invention include the provision of a thermostatic control device which: (a) is marketed as a single unit, yet contains a pair of cooperatively related units; (b) is relatively simple in nature and inexpensive to produce, yet is durable and can be operated for extended periods of time without servicing or mainice tenance; (c) can be quickly and easily controlled by a normally skilled operator; and, (d) operates continuously and serves to maintain the atmosphere in which it is located at a controlled temperature range.

Other objects, advantages and salient features of the present invention will be apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment thereof.

The foregoing objects are attained by providing, as the preferred embodiment of the invention, a device having two thermostats therein controlled by a single adjusting knob. Each thermostat is provided with a series of dial gears, and the control knob is likewise provided with a series of gears, the latter being movable. By properly adjusting these meshing gears, the temperature differential between the two units may be selectively varied, as desired. As an example, the device may be set to a condition wherein the two thermostat units always operate 5 F. apart. Thus, if the lower temperature thermostat were set to F., the higher reading thermostat would be set to F. In this manner, even if the lower reading thermostat should fail or become inoperative, the temperature would only rise to the temperature setting of the higher reading thermostat, i.e., 85 F. in the example mentioned above. A light is connected to the high reading thermostat, and this light will burn continuously as long as the lower reading thermostat is operating. If, however, the lower reading thermostat should fail, the higher reading thermostat will then stop the heat supply burner, and the light will go out, thus indicating to the operator that the lower limit thermostat has broken.

It is possible to incorporate a timer into the thermostatic control unit of the subject invention to thus assure that a preselected temperature range between thermostats will gradually increase in predetermined time intervals. By using such a timing control, the unit will permit the temperature to raise a preselected number of degrees each hour, day, or other time interval selected by the operator.

Referring to the drawings:

FIGURE 1 is a front elevational view of a thermostatic control device in accordance with the principles of the present invention;

FIGURE 2 is a top plan view of the thermostatic control device shown in FIGURE 1;

FIGURE 3 is a front elevational view of a thermostatic control device similar to that of FIGURE 1, but incorporating a timer mechanism;

FIGURE 4 is a top plan view of the thermostatic control device of FIGURE 3;

FIGURES 5 and 6 are fragmentary front elevational views of the timer mechanism utilized in the device of FIGURE 3, shown in various positions;

FIGURE 7 is a fragmentary plan view of an adjustable gear train utilized to operate the subject control devices;

FIGURE 8 is a fragmentary front elevational view of the device of the present invention utilizing a gas operated thermostatic valve means;

FIGURE 9 is a sectional view taken substantially along line 9-9 of FIGURE 8;

FIGURE 10 is a sectional View taken substantially along line 10-10 of FIGURE 8; and

FIGURE 11 is a schematic wiring diagram showing the device of the subject invention connected with a suitable form of heating means.

In accordance with the principles of the present invention, and as will be seen from the accompanying drawings, there is provided a new and novel thermostatic control device generally indicated by the numeral 10, which, in its preferred form, includes a first or operating thermostat mechanism generally designated 12 and a second or limit All of the various components and elements of the device 10 are mounted upon a base mounting plate 16. A series of mounting screws 18 attach the thermostat mechanisms 12 and 14 to the base plate 16, with such mounting screws projecting through outwardly directed flanges on each of the thermostat mechanisms.

Referring now to FIGURES 1 and 2, the first or operating thermostat mechanism 12 includes a thermostatic fluid containing bulb 20, an elongated capillary tube 22 projecting from the bulb, and an electrical switching portion 24 to which the capillary tube is connected. The portion 24 includes a pair of attachment screws 26 to which suitable electric wiring may be connected, in a manner to be presently described. A calibrated dial 28 having appropriately spaced indicia 30 thereon also forms a par-t of the thermostat mechanism 12. A knob 32 projects outwardly from the dial 28 and is either attached directly to the dial itself or to its mounting shaft, to thereby enable the dial to be manually rotated, if desired. A stationary indicating pointer 34 is disposed adjacent the periphery of the dial 28, and thus as the dial rotates, the indicating pointer 34 Will be directed to a particular indicia 30.

In a similar manner, the second or limit control thermostat 14 includes a thermostatic liquid containing bulb 36, an elongated capillary tube 38 extending from the bulb, an electric switch portion 40 to which the capillary tube connects, and a pair of attachment screws 42 to enable electrical leads to be connected to the portion 40. Also, in a similar manner, a dial 44 is provided with indicia 46 thereon, a knob 48 projecting from the dial, and a fixed indicating pointer 50 adjacent the periphery of the dial, whereby as the dial is rotated, the pointer will be directed to a particular indicia 46.

It will be noted that the outer edges of each of the dials 28 and 44 are serrated to thus form the dials into toothed gears, with common teeth being provided on each of such dials. An intermediate cluster drive gear generally designated 52 is disposed between the dials 28 and 44 by being rotatably mounted upon a shaft 54 projecting forwardly from the base 16. The cluster drive gear 52 includes four concentric stacked gears identified respectively, from smallest to largest, as 56, 58, 60 and 62. The purpose of the intermediate cluster drive gear 52 is'to assure that the dials 28 and 44, and hence the thermostat mechanisms 12 and 14 themselves, operate synchronously. To this end, one of the gears of the intermediate cluster drive gear 52 engages the toothed periphery on each of the dials 28 and 44. In the illustrated embodiment, as shown in FIGURE 2, it is the gear 58 which engages the dials, but it will be understood that if dials of a different diameter are utilized, the intermediate cluster drive gear 52 can accommodate such dials merely by being moved relatively thereto, to'thus engage a proper gear with the peripheries of such dials. ,Such relative movement may be accomplished by movement of the shaft 54 itself, by movement of the cluster drive gear 52 relative to the shaft, or by adjustment of the dial plates themselves.

The device 10 is also provided with a signal light or lamp 64, mounted in a base 66, which is provided with a clamp 68 which permits the signal light to be attached to the base portion 16 or to any other suitable attachment means. The signal light 64 is wired into the circuit of the device 10 in a manner to be presently described, and is continually lit while the device is operating properly, to thus give a visual indication of the proper functioning of the device.

As aforesaid, and as will be described more fully hereinafter, the'thermostat mechanisms 12 and 14 do not operate at the same temperature, but rather, a preselected temperature dilferential may be adjusted as desired, so once the differential is set, the intermediate cluster drive gear 52 assures that it will be maintained. Thus, as an example, if the 20- temperature differential is preset between the two thermostat mechanisms, the first control thermostat mechanism generally designated 14.

thermostat 12, which has the lower setting, might. read 80 while the second thermostat 14, which has the highest setting might read 100. Then, through rotation of the intermediate drive gear 52, the first thermostat 12 may be increased to read 90. However, if such an increase occurs, the second thermostat 14 will similarly be increased 10, and will thus read 110, thereby maintaining the preset temperature differential of 20 between the mechanisms.

The operating thermostat 12 is preferably provided with a 2' /z differential between its on and off positions. The high limit thermostat 14 is preferably provided with 21 differential between its on and olf positions. However, the thermostats can be reversed if desired, so that the thermostat with the 5 differential is used as the operating thermostat and the thermostat with the 2 /2 differential is used as the high limit thermostat. If used in this manner, the 5 differential thermostat would be 'set' 5 to below .the setting on the 2- /z dilferential thermostat, and thus the burner being controlled could be given a longer on and off period.

The unit 10, as shown in FIGURES 1 and 2, can be manually operated merely by manually turning one of the knobs 32 and 48. In such an arrangement, the desired heating range, that is, the temperature differential between the mechanisms 12 and 14 would be preset by adjusting the dials 28 and 44 to their desired difference, and then turning one or both of the knobs to move the first dial 28 to the lower temperature of the range, thereby assuring that the second dial 44 will read the upper temperature in the range. In order to permit the dials 28 and 44 to be operated relatively .to one another, it is desirable that the intermediate cluster drive gear 52 be temporarily disengageable from each of the dials.

Of course, such an expedient can be accomplished merely by removing the cluster drive gear 52 from its mounting shaft 54, but it is considered far simpler to provide a mounting screw 76 to hold the cluster drive gear 52 on the shaft, and a compression spring 78 surrounding the screw 76 and being interposed between its head and the upper portion of the cluster drive gear 52. The biasing spring 78 serves to normally press the intermediate cluster drive gear 52 inwardly, so that one of the gears 56, 58, 60 or 62 engages the serrated edges on the dial. However, the biasing effect of the spring 78 may be overcome by manually pulling the cluster drive gear 52 outwardly, in which case the dials 28 and 44 may be freely moved to any desired temperature differential.

As an alternative to the manually operable system previously described, it is possible to incorporate an automatic timer control into the system, in the manner shown in FIGURES 3 and 4. The timer control in these figures is disposed on the right side of the axis XX of FIGURE 4. That portion to the left side of the axis X- X corresponds to the system described in FIGURES 1 and 2, except that a micro-switch 70 having a pivotal switch finger 72 is mounted behind the indicating pointer 34 on the operating thermostat 12, and is thus disposed adjacent the periphery of the dial 28 of the operating thermostat. An adjustable pointer 74 is attached to the operating thermostat 12, and is disposed behind the dial 28, thus projecting outwardly a distance beyond its outer periphery, as shown. Although the pointer 74 may be moved relatively to the dial, to thus position the pointer in alignment with a preselected indicia, such pointer is either operatively or directly connected to the dial 28 for rotation in unison therewith. Thus, if the thermostat dial is moved to gradually increase the temperature in the environment controlled by the device 10, such dial movement will eventually bring the pointer 74 into contact with the switch finger 72, to thereby operate the micro-switch 70 to thereby control operation of a heating unit in the environment being heated, through a wiring system to be presently described.

The automatic timer control on the right side of the axis XX in FIGURE 4 includes a cluster drive gear generally designated 80 mounted upon a shaft 82 projecting from the base plate 16. As with the cluster drive gear 52, the cluster drive gear 80 includes four stepped gear portions, designated respectively from smaller to larger, 84, 86, 88 and 90. A screw 92 and biasing compression spring 94 serve to mount the cluster drive gear 80 on the shaft 82, in the manner previously described in connection with the screw 76 and spring '78.

A timing motor unit 96 is disposed adjacent the cluster drive gear 80 and beneath a motor mounting plate 98. The motor mounting plate 98 is spaced away from the base plate 16 by a series of legs 100, and screws or other suitable fastening devices 102 project through the mounting plate 98 .to attach the same to the terminal ends of the legs 100. The timing motor 96 is attached to its mounting plate 98 by a single pivot mounting bolt 104, which connects at the very end of the .timing motor, and thus permits the entire timing motor to swing or pivot through an are about the bolt 104. A generally U-shaped slot 106 is provided in the mounting plate 98, with such slot having its open end directed toward the cluster drive gear 80. A shaft 108 projects outwardly from the timing motor 96 and through the slot 106. One edge of .the shaft 108 is flatted, as can be best seen in FIGURE 3, to thus assure that a gear mounted upon such a shaft cannot rotate relatively thereto.

An adjustable motor driven cluster drive gear generally designated 110 is mounted on the shaft 108, and is slidable axially therealong. The adjustable motor driven cluster drive gear 110 includes a stacked series of gears, similar to those shown in the cluster drive gears 52 and 80, and such gears are designated respectively, from smallest to largest, 112, 114, 116 and 118. As shown in FIG- URES 4 and 7, axial movement of the cluster drive gear 110 determines which one of the gears 112, 114, 116 or 118 mates with the gear 90 on the cluster drive gear 80-. In this manner, the timing motor 96 can adjustably control the temperature increase of the thermostat mechanisms 12 and 14. For instance, if the smallest gear 112 on the adjustable cluster drive gear 110 mates with the gear 90 on the cluster drive gear 80, the temperature is increased at a rate of, for example, 2 degrees per hour. If the next largest gear 114 mates with the gear 90', the temperature is increased at a rate of 3 degrees per hour. Similarly, if the gear 116 mates with the gear 90, the temperature is increased at the rate of 4 degrees per hour and if the gear 118 mates with the gear 90, the temperature is increased at the rate of 5 degrees per hour.

The timing motor 96 is provided with a projecting leg portion 120 which extends outwardly through a slot 122 at one end of the mounting plate 98. The leg 120' can have a screw 124 or other suitable projection thereon to mount one end of a biasing extension spring 126, as shown in FIGURE 4.'The opposite end of the extension spring is mounted to a member 128 on the second thermostat mechanism 14, which member also serves to mount the indicating pointer 50. By being mounted in such a manner, the spring 126 tends to pull the leg portion 120, and the gear cluster 110 thereon, toward the thermostat mechanisms. In the position shown in FIGURE 5, the gears 118 and 90 are in engagement with one another, and the leg portion 120 is thus moved furthest to the right, thus tensioning the spring 126 to its maximum. In FIG- URE 6, the three respective positions wherein the gears 116, 114 and 112 engage with the gear 90 are illustrated, and it will be noted that the leg portion 120 gradually moves toward the left as the smaller gears on the adjustable cluster drive gear 110 are utilized. This movement to the left is occasioned by the biasing spring 126.

In the system shown in FIGURES 1, 2, 4 and 5, the switching portions 24 and 40 are electrically operated. However, if desired, such systems may be utilized with a gas operating medium rather than an electrical one. A suitable gas valve means is shown in FIGURES. 8-10, with such gas valve means being generally designated 200. The means 200 includes a body 202 adapted to be juxtaposed to the calibrated dials on the thermostat. The body is provided with a gas inlet end 204 and a gas outlet end 206. Interiorly of the body, an upwardly stepped portion 208 and a downwardly stepped portion 210 are provided, with such portions being spaced apart from one another and interconnected by an axially extending portion 212. To permit controlled axial flow of the gas from the inlet end 204 to the outlet end 206, an aperture 216 is provided in the axially extending portion 212. A similar aperture 218 is provided in the walls of the body 202 above and in alignment with the aperture 216, with the upper aperture 218 being threaded. An aperture 214 is provided in the downwardly stepped portion 210 for a purpose to be hereinafter described.

A leaf member 220 is mounted beneath the portion 212 with the forward end of the member lying beneath the aperture 216. Ears 222 are provided at the rear end of the member 220 to pivotally mount the member in such a manner that the forward end can swing upward and downward. The rear end 224 of the member 220 is directed downwardly and a tension spring 226 extends between the end 224 and the body 202 to normally bias the forward end of the member 220 upwardly to contact the undersur face of the portion 212. A projection 228 extends upwardly from the member 220 to be engaged by the base of a conventional thermostatic bellows, shown in dashed lines, and designated 230.

A threaded plug 232 is mounted within the threaded aperture 218 and such plug includes a stub stern 234. A valve plate 235 overlies the aperture 216 and such valve plate includes a first stem 236 directed upwardly toward the stem 234 and a second stem 238 projecting through the aperture 216 to engage the forward end of the member 220. A compression spring 240 surrounds the stems 234 and 236 and extends between the plug 232 and the plate 235 to bias the plate downwardly. The bias of the spring 226 acts upon the member 220 to bias the plate 235 upwardly. It can thus be seen that the plate 235 floats freely within the body 202 with the position of such plate, and hence the flow rate of gas, being determined by the thermostatic bellows 230.

The valve plate 235 has a small hole 242 therein which with the aperture 214 in the downwardly stepped portion 210 serves as a bypass to assure a gas flow to the burner at all times regardless of the position of the plate 235. When the plate 235 is seated, the flame in the burner will be a low or minimum flame. The raising and lowering of the plate 235 is controlled by the thermostatic bulb which is centrally located in the curing barn. The thermostat controls the burner to vary the flame from a minimum to a maximum, with the control being effected by the bellows 230. The gas burners are lit by the operator, and as more heat is desired, more burners are lit, with the thermostat serving to raise the burner flame from low to high. The thermostat can be periodically advanced by the operator until the high setting of 170 F. is reached.

If attention is now directed to FIGURE 11, the manner of connecting the device 10 to a heating unit will be described. A pair of power supply lines L1 and L2 are provided to supply power to the circuit from a suitable power supply. A lead 130 connects the power supply to ground. The lines L1 and L2 extend from the power supply to the respective attachment screws 42 on the high limit thermostat 14. A branch lead 132 extends from power supply line L1 to the burner. Similarly, a lead 134 extends from one of the attachment screws 42 to the burner. The burner is grounded by a lead 136. A pair of leads 138 and 140 extend from the respective attachment screws 26 on the operating thermostat 12 to a relay which controls the burner. It will also be noted that the signal light 64 is connected in series with the power supply line L1.

In operation, the operating thermostat 12 functions to control operation of the burner, since, when the ambient temperature at the thermostatic bulb 20 drops below that value preset on the thermostat 12, a switch in the relay closes to set the burner into operation. Once the temperature reaches the proper level, the circuit in the bulb 20 will be broken, and the switch in the relay will once again open, thereby halting operation of the burner. The thermostat 14 serves as a high limit control device, to assure that the temperature in the atmosphere being heated cannot exceed a preselected high value. If, for example, the thermostat mechanism 12 were to break or otherwise become inoperative, the burner might continue to run and the temperature might thereby continue to rise. If, however, that temperature reaches the setting of thermostat mechanism 14, the switch in the relay will be opened, thereby halting operation of the burner. It will be noted that the signal light 64 is tied into the circuit of the high limit thermostat mechanism 14. In this manner, since the switch in the relay is normally closed, the light 64 normally burns, thereby indicating to an operator that the device 10 is functioning properly. When and if the thermostat mechanism 12 should become inoperative, and it becomes necessary for the thermostat mechanism 14 to open the switch in the relay, power to the light is interrupted, and the light will no longer burn. This will serve to indicate to an operator, or a watchman checking the building wherein the device is located, that the operating thermostat mechanism 12 has failed.

The wiring diagram previously described in connection with FIGURE ll corresponds to that utilized in FIGURES 1 and 2. However, the same wiring diagram is applicable to the timer controlled embodiment of FIGURES 3 and 4, the sole difference being the addition of the timing motor 96 and the micro-switch 70, as also illustrated in FIGURE 11.

With the operation of the device 10 now firmly in mind from the foregoing discussion, a brief description will be given of the manner in which the device 10 can be used in its preferred application, namely, in the curing of tobacco. The device 10 is placed outside the barn where the tobacco is curing and the capillary tubes 22 and 38 run through the wall of the barn to enable the thermostatic bulbs and 36 to sense temperature conditions within the barn. The device 10 is energized by plugging the same into a 110 volt wall receptacle, thus providing power to the input lines L1 and L2. Preferably, the thermostat mechanisms '12 and 14 are set five degrees apart, with a preferred temperature for the mechanism 12 being 85 and a preferred temperature for the mechanism 14 being 90. These temperatures are maintained for approximately 24 hours during which the tobacco is cured from a green color to a yellow color. Then, the timing motor 96 can be put into operation, to gradually increase the temperature within the barn to small increments of a few degrees per hour. Since the maximum temperature desired is approximatelyl60, the adjustable pointer 74 is moved into alignment with the 160 indicia. The micro-switch 71 is normally closed, thus assuring that power from the input line will flow to the timing motor 96. However, when the temperature has increased to the maximum desired, as for example, 160, the adjustable pointer 74 will strike the spring finger 72 on the switch 70 and will thereby open the switch 70. When this occurs, the fixed high temperature limit will have been reached and the heat cannot be further advanced.

While the device 10 of the present invention has been described as having a pair of thermostat mechanisms assembled together to form a single unit, it will be understood that the principles of the present invention are equally applicable to entirely separate and distinct single thermostat mechanisms. That is, if a person already owned a suitable type of single, manually controlled thermostat mechanism, he would not need to purchase an entire device 10 having a double pair of thermostat mechanisms therein,

and instead, could purchase a single thermostat type unit. Such a unit would, of course, include an intermediate cluster drive gear such as that shown at 52, so that the two thermostat units could be coupled together in a cooperative manner, to operate synchronously and to define a desired heating range. Such a combination of single units could be manually operated in the manner previously described, or could be operated by a timing motor 96 in the manner previously described.

After reading the foregoing detailed description, it will be apparent that the objects set forth at the outset of the specification have been successfully achieved.

What is claimed is:

1. A thermostatic control device for use in controlling a heating unit having a relay means therein, said device comprising:

a first thermostat mechanism connected to said relay means and responsive to the temperatures produced by said heating unit to thereby operate said relay means;

a second thermostat mechanism operable in synchronism with said first thermostat mechanism and connected to said relay means;

said first and second thermostat mechanism being adjustably interconnected to maintain a preselected temperature differential therebetween which defines a desired heating range;

said second thermostat mechanism defining the upper limit of said range;

a signal light connected to said second thermostat mechanism to visually indicate when said device is in operation; and

means for presetting said first and second thermostat mechanisms to a desired heating range;

said first thermostat mechanism normally controlling the operation of said heating unit;

said second thermostat mechanism being operative, in

the event of failure of said first thermostat mechanism, to stop operation of said heating unit;

said signal light normally operating continuously, but

being rendered inoperative when said second thermostat mechanism stops said heating unit to thereby visually indicate that said first thermostat mechanism has failed.

2. A thermostatic control device, as defined in claim 1, wherein each of said thermostat mechanisms includes a calibrated dial having a toothed periphery.

3. A thermostatic control device as defined in claim 2, wherein said thermostat mechanisms are interconnected by an intermediate gear means disposed between said dials and in meshing engagement with the toothed peripheries thereof.

4. A thermostatic control device as defined in claim 3, wherein said intermediate gear means assures that said first and second thermostat mechanisms operate synchronously, but wherein said intermediate gear means can be selectively unmeshed from said dials to permit said dials to be adjusted relatively to one another.

5. A thermostatic control device as defined in claim 3,

wherein said means includes a timing motor and a driving 7 gear arrangement operated by said timing motor.

6. A thermostatic control device as defined in claim 5, wherein said timing motor is swingably attached to a mounting plate and wherein a shaft projects from said motor for mounting at least a part of said driving gear arrangement.

7. A thermostatic control device as defined in claim 6 wherein a cluster drive gear having a plurality of stacked gears, gradually increasing in size, is slidably mounted upon said shaft for rotation therewith and for axial movement therealong.

8. A thermostatic control device as defined .in claim 7 wherein said cluster drive gear is operatively connected to Said thermostat mechanisms for incrementally increasing 9 their settings in response to operation of said timing motor.

9. A thermostatic control device as defined in claim 8 wherein said incremental increasing is responsive to which of said gears on said cluster drive gear is connected in driving engagement with said thermostat mechanisms.

10. A thermostatic control device as defined in claim 9, .but further characterized by a switch means operatively associated with said timing motor for turning the same on and off and a switch operating means connected to said first thermostat mechanism.

11. A thermostatic control device as defined in claim 10, wherein said switch operating means includes a pointer adjustably attached to said first thermostat dial and projecting beyond its periphery whereby rotation of said dial will swing said pointer into contacting condition with said switch means for operation thereof.

12. In combination with a heating unit having an operating motor controlled by a relay means, a thermostatic control device for selectively controlling operation of said heating unit, said device comprising:

an operating thermostat including a first temperature responsive liquid containing bulb, an elongated capillary tube extending from said first bulb, and a first electrical unit controlled by said first bulb and having a first calibrated dial thereon;

a limit control thermostat including a second temperature responsive liquid containing bulb, an elongated capillary tube extending from said second bulb, and a second electrical unit controlled by said second bulb and having a second calibrated dial thereon;

each of said calibrated dials having commonly serrated edges providing peripheral gear teeth;

an intermediate gear means disposed between said dials in engagement with the teeth thereon to thus assure that said dials operate in synchronism;

a drive gear means disposed in engagement with one of said dial edges;

a timing motor means having a projecting shaft which rotates at a preselected rate;

a motor operated gear means upon said shaft;

said motor operated gear means engaging said drive gear means to rotate the same and hence to rotate said dials as said timing motor operates;

a switch means electrically connected with said timing motor;

a switch operating member rotatable in unison with said first dial to control said switch means; and

a signal light electrically connected with said limit control thermostat mechanism and being illuminated as long as said operating thermostat mechanism is functioning;

said operating thermostat mechanism being electrically connected to said relay means to control operation of said heating unit;

said limit control thermostat mechanism also being electrically connected to said relay means but being normally inoperative while said operating thermostat mechanism is functioning;

said limit control thermostat mechanism becoming operative, if said operating thermostat mechanism fails, to shut down said heating unit operating motor;

said signal light being de-energized when said limit con trol thermostat mechanism shuts down said heating unit operating motor;

said thermostat mechanisms normally having a preset temperature differential therebetween;

said timing motor being operative to incrementally increase the temperature settings of said thermostat mechanisms while maintaining said preset temperature diiferential therebetween;

said switch operating member being adjustable to a preset temperature at which said incremental temperature increases are to terminate;

said switch operating member engaging said switch means when said preset temperature is reached, thereby stopping said timing motor and thus terminating said incremental temperature increases.

13. The combination of claim 12 wherein each of said gear means includes a plurality of stacked gears, gradually increasing in size.

14. The combination of claim 13 wherein said motor operated gear means is slidable along its shaft to selectively adjust which of its gears is to mate with said drive gear means and to thereby selectively determine the rate of incremental temperature increase.

15. The combination of claim 14 but further characterized by a biasing means normally urging said motor operated gear means into engagement with said drive gear means.

16. In a heat control system having a pair of thermostats, the invention comprising:

thermostats each having a calibrated dial with a serrated peripheral edge;

gear means interposed between and in meshing engagement with said dial serrated edges;

said gear means being rotatable to drive said dials synchronously in opposite directions;

one of said thermostats normally controlling a heating unit;

the other of said thermostats being operative, in the event of failure of said one thermostat, to stop operation of said heating unit;

said gear means including a plurality of superposed gears, with one of said gears being selectively engageable with said dial edges to effect said synchronous movement.

17. The invention defined in claim 16 but further characterized by a signal light connected to said other thermostat.

18. The invention defined in claim 17 wherein said signal light normally operates continuously to visually indicate that said one thermostat is operative, but being rendered inoperative when said one thermostat fails.

References Cited UNITED STATES PATENTS 2,518,021 8/1950 Keay 2372 2,736,499 2/1956 Hazen 23694 X 2,819,844 1/1958 Dennick 23644 WILLIAM J. WYE, Primary Examiner. ALDEN D. STEWART, Assistant Examiner. 

1. A THERMOSTATIC CONTROL DEVICE FOR USE IN CONTROLLING A HEATING UNIT HAVING A RELAY MEANS THEREIN, SAID DEVICE COMPRISING: A FIRST THERMOSTAT MECHANISM CONNECTED TO SAID RELAY MEANS AND RESPONSIVE TO THE TEMPERATURES PRODUCED BY SAID HEATING UNIT TO THEREBY OPERATE SAID RELAY MEANS; A SECOND THERMOSTAT MECHANISM OPERABLE IN SYNCHRONISM WITH SAID FIRST THERMOSTAT MECHANISM AND CONNECTED TO SAID RELAY MEANS; SAID FIRST AND SECOND THERMOSTAT MECHANISM BEING ADJUSTABLY INTERCONNECTED TO MAINTAIN A PRESELECTED TEMPERATURE DIFFERENTIAL THEREBETWEEN WHICH DEFINES A DESIRED HEATING RANGE; SAID SECOND THERMOSTAT MECHANISM DEFINING THE UPPER LIMIT OF SAID RANGE; A SIGNAL LIGHT CONNECTED TO SAID SECOND THERMOSTAT MECHANISM TO VISUALLY INDICATE WHEN SAID DEVICE IS IN OPERATION; AND MEANS FOR PRESETTING SAID FIRST AND SECOND THERMOSTAT MECHANISMS TO A DESIRED HEATING RANGE; SAID FIRST THERMOSTAT MECHANISM NORMALLY CONTROLLING THE OPERATION OF SAID HEATING UNIT; SAID SECOND THERMOSTAT MECHANISM BEING OPERATIVE, IN THE EVENT OF FAILURE OF SAID FIRST THERMOSTAT MECHANISM, TO STOP OPERATION OF SAID HEATING UNIT; SAID SIGNAL LIGHT NORMALLY OPERATING CONTINUOUSLY, BUT BEING RENDERED INOPERATIVE WHEN SAID SECOND THERMOSTAT MECHANISM STOPS SAID HEATING UNIT TO THEREBY VISUALLY INDICATE THAT SAID FIRST THERMOSTAT MECHANISM HAS FAILED. 